Electroplating



Patented Apr. 23, 1940 PATENT OFFICE ELECTROPLATING Lionel Cinamon, New York, and Samuel Sklarew, Yonkers, N. Y., assignors to Special Chemicals goal-1km, New York, N. Y., a corporation of New No Drawing. Application June 29, 1988, Serial No. 216,474

2 Claims. (Cl. 204-2) Our invention relates generally to electroplating and more particularly, to an electroplating composition and bath.

One of the objects of our invention is to pro- 5 vide a novel electroplating composition and bath of the character described which is adapted to electrodeposit a gold-colored alloy plate.

Another object of our invention is to provide a novel electroplating composition and bath which will deposit a gold-colored alloy plate for long periods of time without any appreciable change in the color of the plate.

A further object of our invention is to provide a novel electroplating composition and bath which will deposit a gold-colored plate of the character described at relatively low temperatures.

Still another object of our invention is to provide a novel electroplating composition and bath which will deposit a gold-colored alloy plate of the character described with consistently satis factory results and in a simple and inexpensive manner.

Other objects of our invention will in part be 25 obvious and inpart hereinafter pointed out.

In accordance with our invention a dry composition that is, an electroplating bath composition, may be prepared by making a mixture of copper salts, zinc salts, tin salts, and an alkaline cyanide. This composition may then be added to water or any other suitable solvent to form an electroplating bath solution. We have also found that our novel bath solution may be formed by adding copper salts, zinc salts, tin 35 salts and an alkaline'cyanide either independently or in any possible combination or combinations thereof to the solvent without first mixing the same. In preparing the electroplating bath composition, addition agents such as those here- 40 inafter described may also be employed.

We have found that when an electroplating bath solution, prepared in accordance with our invention, contains a copper content of from 4 about 2.8grams per gallon to the saturation point of the copper salts used, a zinc content of comprising the plating composition will dissolve in the solvent employed. Some of these salts are:

Sodium stannate Na2SnOa-3H2O Sufficient alkaline cyanide should be included in the dry bath composition to insure a free or uncombined alkaline cyanide content of from 1 to 5 ounces per gallon of plating solution. We have found that the most satisfactory results are obtained by the presence of from 2 to 3 ounces of free alkaline cyanide per gallon.

In practicing our invention, the pH value of our plating solution must be maintained between 12.7 and 13.1.

We have found that while electrodepositing a gold-colored alloy plate from our plating solution, the ratio of the tin content of the bath solution to the copper content of the bath solution increases. Also it was found while electrodepositing our plate that the ratio of the zinc content of the bath solution to the copper content of the bath solution decreases.

An alloy plate comprising copper, zinc and tin may be electrodeposited from our bath solution by using either insoluble or soluble anodes. The soluble anodes may be either in the form of an alloy of copper, zinc and tin or individual anodes 5 of these three metals.

In connection with the practice of our invention a plating voltage of from 4 to 9 volts and a current density of from 25qto 60 amperes per square foot has been found to be satisfactory. Where soluble anodes of copper, zinc andtin are used, the current density may be suitably adjusted for proper corrosion in accordance with the shade of gold desired to be obtained. The temperature of the bath may be maintained from 20 to 75 C. We have found that the most satisfactory results are obtained from 20 to 25 C. The rate of deposition at room temperature and 5 volts plating voltage is from 0.00035 to 0.0006 inch per hour. As the temperature is raised, the rate of electrodeposition will be proportionately increased.

Also by our invention, various addition agents as brighteners and for conductivity such as those listed below, may be used in single, double or multiple combination in our dry bath composition.

Trisodium phosphate NasPOrHaO Sodium pyrophosphate NarPaOrlOHzO Rochelle salt NaKCsHsOs Sodium bisulflte NaHSOs Sodium sulfate NaaSO4 Sodium carbonate NazCO: Sodium arsenite NaAsOz Arsenious acid AszOs Sodium phenylate NaCsI-IsO Goulac (tailings from sulphite liquor concentrate in preparation of wood pulp).

Sodium thiosulfate NaaSaOz Soda alum. NaAl(SO4)=-12H=0 Dextrose n-csrruos Sodium oxalate Nazca-O4 Potassium ferrocyanide K4Fe(CN)o Cadmium oxide CdO Sodium citrate zimcsmoq-imlo The above listed addition salts are representative members of their groups. For example, Rochelle salt is a member of the tartrate group and is merely given as an example of such. with other tartrates, such as ammonium, copper, magnesium, zinc or tin tartrate, the plating bath will function equally well. If, upon adding any of the above addition agents, the alkalinity of the bath falls without the pH range of 12.7 to 13.1 sodium hydroxide may be added to restore the pH value to within the said range.

We have found that satisfactory results are obtained by using the following addition salts for brightening or conductivity either singly, doubly or in multiple combination in the ranges .set forth.

Addition agents The following are specific examples of dry bath compositions which we have found to give good results, it being understood that they are in no way limitative. The weights given are for use with 1 gallon of a plating bath.

Example IV OM08) ZnO ZnBOe'lI-hO NaaSnOa- NaCN In accordance with our invention, a bright copper-zinc-tin alloy plate of gold color can be electro-deposited from our bath composition at room temperature for periods of time up to about five minutes. After this the plate would become cloudy. The same clouding eflect will also occur in shorter periods of time when the temperature of the plating bath is raised above room temperature.

Plates which have become heavily clouded present a novel appearance resembling a twotoned changeable-colored velvet and may be employed on encased visible objects such as watch dials, in order to produce an unusual and desirable effect. when this heavily clouded plate is lacquered, it will become evenly bun-colored. when it is desired to provide a relatively heavy bright plate, and during the electrodeposition of the same, the plate becomes cloudy, it may be easily buffed to a high lustre.

.By our invention as herein described, we have been able to produce an electroplated copperzinc-tin alloy characterized by its gold color. We have also found that our alloy may be plated for a long period of time without appreciably changing its shade. Also our alloy plate forms a substantially uniform deposit on irregular surfaces and may be electrodeposited for several hours without treeing or forming mounds of the alloy, this being due to the inherently high throwing power or our bath solution. Also our gold-colored alloy is characterized by its hardness and density. Also it will withstand considerable handling without appreciable staining or tarnishing. It is highly resistant to many acids and salt solutions such as, for example, 5% glacial acetic acid, 85% phosphoric acid, 6N to 3217 sulphuric acid, 4N to 12N hydrochloric acid, a saturated solution of potassium permanganate. It is slowly attacked by a 10% solution of sodium hydroxide and may be dissolved by a 3N to 18N nitric acid or by a concentrated solution of ammonium hydroxide. Also it may be readily plated over a wide variety of base metals as. for example, copper, brass, bronze, iron, steel, nickel, zinc die cast, zinc and silver.

, It will, thus be seen that there is provided a 188.50 Ema/B lion composition, bath and process by means of which A -ai the several objects of this invention are achieved, and which are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, we claim as new and desire to secure by Letters Patent:

1. A process of electrodeposlting a gold-colored copper-zinc-tin alloy plate comprising passing a current through an aqueous alkali cyanide bath solution containing copper salts, zinc salts, and tin salts, the quantities of said salts being such that the metallic contents of one gallon of said solution will be from about 2.8 grams to saturation of copper, from about 7.7 to 40 grams of zinc and from about 3.7 to 59 grams of tin and having a tree alkali cyanide content of from about 1 to 5 ounces per gallon of solution while maintaining the pH value of said solution from about 12.7 to 13.1. 7

2. An electroplating bath for depositing a goldcolored alloy plate of copper-zinc and tin, said bath comprising an aqueous alkali cyanide solu tion of copper, zinc and tin salts having a free alkali cyanide content of from about 1 to 5 ounces per gallon of solution, the pH value of said solution being from about 12.7 to 13.1, said bath having metallic contents per gallon of solution of from about 2.8 grams to saturation of copper, from about 7.7 to 40 grams of zinc, and from about 3.7 to 59 grams of tin.

LIONEL CINAMON. SAIMIUEL SKLAREW. 

